/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package me.kuku.utils;

import java.io.Serializable;

/**
 * <p>Operations on <code>Object</code>.</p>
 *
 * <p>This class tries to handle <code>null</code> input gracefully.
 * An exception will generally not be thrown for a <code>null</code> input.
 * Each method documents its behaviour in more detail.</p>
 *
 * @author <a href="mailto:nissim@nksystems.com">Nissim Karpenstein</a>
 * @author <a href="mailto:janekdb@yahoo.co.uk">Janek Bogucki</a>
 * @author Daniel L. Rall
 * @author Stephen Colebourne
 * @author Gary Gregory
 * @author Mario Winterer
 * @author <a href="mailto:david@davidkarlsen.com">David J. M. Karlsen</a>
 * @since 1.0
 * @version $Id: ObjectUtils.java 594336 2007-11-12 22:54:02Z bayard $
 */
public class ObjectUtils {

	/**
	 * <p>Singleton used as a <code>null</code> placeholder where
	 * <code>null</code> has another meaning.</p>
	 *
	 * <p>For example, in a <code>HashMap</code> the
	 * {@link java.util.HashMap#get(java.lang.Object)} method returns
	 * <code>null</code> if the <code>Map</code> contains
	 * <code>null</code> or if there is no matching key. The
	 * <code>Null</code> placeholder can be used to distinguish between
	 * these two cases.</p>
	 *
	 * <p>Another example is <code>Hashtable</code>, where <code>null</code>
	 * cannot be stored.</p>
	 *
	 * <p>This instance is Serializable.</p>
	 */
	public static final Null NULL = new Null();

	/**
	 * <p><code>ObjectUtils</code> instances should NOT be constructed in
	 * standard programming. Instead, the class should be used as
	 * <code>ObjectUtils.defaultIfNull("a","b");</code>.</p>
	 *
	 * <p>This constructor is public to permit tools that require a JavaBean instance
	 * to operate.</p>
	 */
	public ObjectUtils() {
		super();
	}

	// Defaulting
	//-----------------------------------------------------------------------
	/**
	 * <p>Returns a default value if the object passed is
	 * <code>null</code>.</p>
	 *
	 * <pre>
	 * ObjectUtils.defaultIfNull(null, null)      = null
	 * ObjectUtils.defaultIfNull(null, "")        = ""
	 * ObjectUtils.defaultIfNull(null, "zz")      = "zz"
	 * ObjectUtils.defaultIfNull("abc", *)        = "abc"
	 * ObjectUtils.defaultIfNull(Boolean.TRUE, *) = Boolean.TRUE
	 * </pre>
	 *
	 * @param object  the <code>Object</code> to test, may be <code>null</code>
	 * @param defaultValue  the default value to return, may be <code>null</code>
	 * @return <code>object</code> if it is not <code>null</code>, defaultValue otherwise
	 */
	public static Object defaultIfNull(Object object, Object defaultValue) {
		return object != null ? object : defaultValue;
	}

	/**
	 * <p>Compares two objects for equality, where either one or both
	 * objects may be <code>null</code>.</p>
	 *
	 * <pre>
	 * ObjectUtils.equals(null, null)                  = true
	 * ObjectUtils.equals(null, "")                    = false
	 * ObjectUtils.equals("", null)                    = false
	 * ObjectUtils.equals("", "")                      = true
	 * ObjectUtils.equals(Boolean.TRUE, null)          = false
	 * ObjectUtils.equals(Boolean.TRUE, "true")        = false
	 * ObjectUtils.equals(Boolean.TRUE, Boolean.TRUE)  = true
	 * ObjectUtils.equals(Boolean.TRUE, Boolean.FALSE) = false
	 * </pre>
	 *
	 * @param object1  the first object, may be <code>null</code>
	 * @param object2  the second object, may be <code>null</code>
	 * @return <code>true</code> if the values of both objects are the same
	 */
	public static boolean equals(Object object1, Object object2) {
		if (object1 == object2) {
			return true;
		}
		if ((object1 == null) || (object2 == null)) {
			return false;
		}
		return object1.equals(object2);
	}

	/**
	 * <p>Gets the hash code of an object returning zero when the
	 * object is <code>null</code>.</p>
	 *
	 * <pre>
	 * ObjectUtils.hashCode(null)   = 0
	 * ObjectUtils.hashCode(obj)    = obj.hashCode()
	 * </pre>
	 *
	 * @param obj  the object to obtain the hash code of, may be <code>null</code>
	 * @return the hash code of the object, or zero if null
	 * @since 2.1
	 */
	public static int hashCode(Object obj) {
		return (obj == null) ? 0 : obj.hashCode();
	}

	// Identity ToString
	//-----------------------------------------------------------------------
	/**
	 * <p>Gets the toString that would be produced by <code>Object</code>
	 * if a class did not override toString itself. <code>null</code>
	 * will return <code>null</code>.</p>
	 *
	 * <pre>
	 * ObjectUtils.identityToString(null)         = null
	 * ObjectUtils.identityToString("")           = "java.lang.String@1e23"
	 * ObjectUtils.identityToString(Boolean.TRUE) = "java.lang.Boolean@7fa"
	 * </pre>
	 *
	 * @param object  the object to create a toString for, may be
	 *  <code>null</code>
	 * @return the default toString text, or <code>null</code> if
	 *  <code>null</code> passed in
	 */
	public static String identityToString(Object object) {
		if (object == null) {
			return null;
		}
		StringBuffer buffer = new StringBuffer();
		identityToString(buffer, object);
		return buffer.toString();
	}

	/**
	 * <p>Appends the toString that would be produced by <code>Object</code>
	 * if a class did not override toString itself. <code>null</code>
	 * will throw a NullPointerException for either of the two parameters. </p>
	 *
	 * <pre>
	 * ObjectUtils.identityToString(buf, "")            = buf.append("java.lang.String@1e23"
	 * ObjectUtils.identityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa"
	 * ObjectUtils.identityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa")
	 * </pre>
	 *
	 * @param buffer  the buffer to append to
	 * @param object  the object to create a toString for
	 * @since 2.4
	 */
	public static void identityToString(StringBuffer buffer, Object object) {
		if (object == null) {
			throw new NullPointerException("Cannot get the toString of a null identity");
		}
		buffer.append(object.getClass().getName())
				.append('@')
				.append(Integer.toHexString(System.identityHashCode(object)));
	}

	/**
	 * <p>Appends the toString that would be produced by <code>Object</code>
	 * if a class did not override toString itself. <code>null</code>
	 * will return <code>null</code>.</p>
	 *
	 * <pre>
	 * ObjectUtils.appendIdentityToString(*, null)            = null
	 * ObjectUtils.appendIdentityToString(null, "")           = "java.lang.String@1e23"
	 * ObjectUtils.appendIdentityToString(null, Boolean.TRUE) = "java.lang.Boolean@7fa"
	 * ObjectUtils.appendIdentityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa")
	 * </pre>
	 *
	 * @param buffer  the buffer to append to, may be <code>null</code>
	 * @param object  the object to create a toString for, may be <code>null</code>
	 * @return the default toString text, or <code>null</code> if
	 *  <code>null</code> passed in
	 * @since 2.0
	 * @deprecated The design of this method is bad - see LANG-360. Instead, use identityToString(StringBuffer, Object).
	 */
	public static StringBuffer appendIdentityToString(StringBuffer buffer, Object object) {
		if (object == null) {
			return null;
		}
		if (buffer == null) {
			buffer = new StringBuffer();
		}
		return buffer
				.append(object.getClass().getName())
				.append('@')
				.append(Integer.toHexString(System.identityHashCode(object)));
	}

	public static String toString(Object obj) {
		return obj == null ? "" : obj.toString();
	}

	public static String toString(Object obj, String nullStr) {
		return obj == null ? nullStr : obj.toString();
	}

	// Min/Max
	//-----------------------------------------------------------------------
	/**
	 * Null safe comparison of Comparables.
	 *
	 * @param c1  the first comparable, may be null
	 * @param c2  the second comparable, may be null
	 * @return
	 *  <ul>
	 *   <li>If both objects are non-null and unequal, the lesser object.
	 *   <li>If both objects are non-null and equal, c1.
	 *   <li>If one of the comparables is null, the non-null object.
	 *   <li>If both the comparables are null, null is returned.
	 *  </ul>
	 */
	public static Object min(Comparable c1, Comparable c2) {
		if (c1 != null && c2 != null) {
			return c1.compareTo(c2) < 1 ? c1 : c2;
		} else {
			return c1 != null ? c1 : c2;
		}
	}

	/**
	 * Null safe comparison of Comparables.
	 *
	 * @param c1  the first comparable, may be null
	 * @param c2  the second comparable, may be null
	 * @return
	 *  <ul>
	 *   <li>If both objects are non-null and unequal, the greater object.
	 *   <li>If both objects are non-null and equal, c1.
	 *   <li>If one of the comparables is null, the non-null object.
	 *   <li>If both the comparables are null, null is returned.
	 *  </ul>
	 */
	public static Object max(Comparable c1, Comparable c2) {
		if (c1 != null && c2 != null) {
			return c1.compareTo(c2) >= 0 ? c1 : c2;
		} else {
			return c1 != null ? c1 : c2;
		}
	}

	// Null
	//-----------------------------------------------------------------------
	/**
	 * <p>Class used as a null placeholder where <code>null</code>
	 * has another meaning.</p>
	 *
	 * <p>For example, in a <code>HashMap</code> the
	 * {@link java.util.HashMap#get(java.lang.Object)} method returns
	 * <code>null</code> if the <code>Map</code> contains
	 * <code>null</code> or if there is no matching key. The
	 * <code>Null</code> placeholder can be used to distinguish between
	 * these two cases.</p>
	 *
	 * <p>Another example is <code>Hashtable</code>, where <code>null</code>
	 * cannot be stored.</p>
	 */
	public static class Null implements Serializable {
		/**
		 * Required for serialization support. Declare serialization compatibility with Commons Lang 1.0
		 *
		 * @see java.io.Serializable
		 */
		private static final long serialVersionUID = 7092611880189329093L;

		/**
		 * Restricted constructor - singleton.
		 */
		Null() {
			super();
		}

		/**
		 * <p>Ensure singleton.</p>
		 *
		 * @return the singleton value
		 */
		private Object readResolve() {
			return ObjectUtils.NULL;
		}
	}

}
